Registration of coronary sinus catheter image

ABSTRACT

Cardiac catheterization is carried out by importing image data of a heart of a living subject into an image-processing computer system, representing the image data as a first model of the heart and the coronary sinus in a first coordinate space, and introducing a probe into the coronary sinus. Thereafter fluoroscopic image data of the probe are used to prepare a second model of the coronary sinus in a second coordinate space, and the first model is transformed into the second coordinate space by placing the coronary sinus of the second model in registration with the coronary sinus of the first model.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to cardiac physiology. More particularly, thisinvention relates to the evaluation of electrical propagation in theheart.

2. Description of the Related Art

The meanings of certain acronyms and abbreviations used herein are givenin Table 1.

TABLE 1 Acronyms and Abbreviations CS Coronary Sinus LAO Left AnteriorOblique RAO Right Anterior Oblique CT Computed Tomography MRI MagneticResonance Image

Cardiac arrhythmias such as atrial fibrillation are an important causeof morbidity and death. Commonly assigned U.S. Pat. No. 5,546,951, andU.S. Pat. No. 6,690,963, both issued to Ben Haim and PCT application WO96/05768, all of which are incorporated herein by reference, disclosemethods for sensing an electrical property of heart tissue, for example,local activation time, as a function of the precise location within theheart. Data are acquired with one or more catheters having electricaland location sensors in their distal tips, which are advanced into theheart. Methods of creating a map of the electrical activity of the heartbased on these data are disclosed in commonly assigned U.S. Pat. No.6,226,542, and U.S. Pat. No. 6,301,496, both issued to Reisfeld, whichare incorporated herein by reference. As indicated in these patents,location and electrical activity is typically initially measured onabout 10 to about 20 points on the interior surface of the heart. Thesedata points are then generally sufficient to generate a preliminaryreconstruction or map of the cardiac surface. The preliminary map isoften combined with data taken at additional points in order to generatea more comprehensive map of the heart's electrical activity. Indeed, inclinical settings, it is not uncommon to accumulate data at 100 or moresites to generate a detailed, comprehensive map of heart chamberelectrical activity. The generated detailed map may then serve as thebasis for deciding on a therapeutic course of action, for example,tissue ablation, to alter the propagation of the heart's electricalactivity and to restore normal heart rhythm.

Catheters containing position sensors may be used to determine thetrajectory of points on the cardiac surface. These trajectories may beused to infer motion characteristics such as the contractility of thetissue. As disclosed in U.S. Pat. No. 5,738,096, issued to Ben Haim,which is incorporated herein in its entirety by reference, mapsdepicting such motion characteristics may be constructed when thetrajectory information is sampled at a sufficient number of points inthe heart.

Electrical activity at a point in the heart is typically measured byadvancing a multiple-electrode catheter to measure electrical activityat multiple points in the heart chamber simultaneously. A record derivedfrom time varying electrical potentials as measured by one or moreelectrodes is known as an electrogram. Electrograms may be measured byunipolar or bipolar leads, and are used, e.g., to determine onset ofelectrical propagation at a point, known as local activation time.

Currently, large amounts of anatomical and functional data are gatheredduring catheter-based cardiac procedures. Maintaining alignment of thisdata with the actual position of the patient's heart and understandingthe relationship of the catheter to anatomic structures are bothimportant to the success of the procedure. In one approach the catheteris registered to images taken by another modality.

An example of this approach is proposed in U.S. Pat. No. 7,720,520 toWillis. A reference catheter or reference element is placed in contactwith the anatomical body. A physical structure within a navigationalcoordinate system is located using the reference elements or referencecatheter. An image reference within an image coordinate corresponding tothe physical structure is located. Location of the image reference canbe accomplished, e.g., by displaying the medical image andelectronically marking the displayed image reference, or byautomatically locating image data corresponding to the image reference.The navigational and image coordinate systems are then registered basedon the location of the physical structure within the navigationalcoordinate system and the location of the image reference within theimage coordinate system, which allows graphical information to be mergedwith the medical image data.

SUMMARY OF THE INVENTION

According to disclosed embodiments of the invention, a reconstruction ofthe heart is prepared prior to catheterization from cardiac image data,such as CT or MRI data. The reconstruction takes into considerationmotion of the cardiac structures such as the coronary sinus due tocardiac and patient motion. Using the reconstruction, the coronary sinusis catheterized and reconstructed using fluoroscopic image data. Thereconstruction of the coronary sinus is placed in registration with thereconstruction of the heart, so that the resulting image has acoordinate space consistent with that of a functional electroanatomicimages of the heart that may be displayed or generated, for example aCARTO map. Cardiac structures of interest may then be identified on thefunctional electroanatomic image by an operator.

There is provided according to embodiments of the invention a method,which is carried out by importing image data of a heart of a livingsubject into an image-processing computer system, representing the imagedata as a first model of the heart and the coronary sinus in a firstcoordinate space, and introducing a probe into the coronary sinus.Thereafter, the method is further carried out acquiring fluoroscopicimage data of the probe, using the fluoroscopic image data to prepare asecond model of the coronary sinus in a second coordinate space, andtransforming the first model into the second coordinate space by placingthe coronary sinus of the second model in registration with the coronarysinus of the first model.

The image data is obtained by computed tomography or magnetic resonanceimaging of the heart.

According to an aspect of the method, the first model is a 3-dimensionalmodel.

According to still another aspect of the method, preparing a secondmodel includes reconstructing a 2-dimensional path of the probe.

According to an additional aspect of the method, preparing a secondmodel includes estimating a 3-dimensional path of the probe from the2-dimensional path.

Another aspect of the method includes locating a cardiac structure inthe transformed first model in the second coordinate space.

There is further provided according to embodiments of the invention anapparatus, including a cardiac catheter adapted for introduction into acoronary sinus of a heart of a living subject, a display, and aprocessor. The processor is cooperative with a fluoroscopic imagingdevice for performing a method, which is carried out by importing imagedata of the heart into an image-processing computer system, representingthe image data as a first model of the heart and the coronary sinus in afirst coordinate space, and introducing a probe into the coronary sinus.Thereafter, the method is further carried out acquiring fluoroscopicimage data of the probe, using the fluoroscopic image data to prepare asecond model of the coronary sinus in a second coordinate space, andtransforming the first model into the second coordinate space by placingthe coronary sinus of the second model in registration with the coronarysinus of the first mode.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present invention, reference is madeto the detailed description of the invention, by way of example, whichis to be read in conjunction with the following drawings, wherein likeelements are given like reference numerals, and wherein:

FIG. 1 is a pictorial illustration of a system for performing cardiaccatheterization procedures, which is constructed and operative inaccordance with an embodiment of the invention;

FIG. 2 is a flow-chart of a method of registration of cardiac imagesusing a coronary sinus catheter in accordance with an embodiment of theinvention; and

FIG. 3 is a composite image illustrating a stage in the process ofcoronary sinus reconstruction as applied to a 3-dimensional model of theheart, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the various principles ofthe present invention. It will be apparent to one skilled in the art,however, that not all these details are necessarily needed forpracticing the present invention. In this instance, well-known circuits,control logic, and the details of computer program instructions forconventional algorithms and processes have not been shown in detail inorder not to obscure the general concepts unnecessarily.

Aspects of the present invention may be embodied in software programmingcode, which is typically maintained in permanent storage, such as acomputer readable medium. In a client/server environment, such softwareprogramming code may be stored on a client or a server. The softwareprogramming code may be embodied on any of a variety of knownnon-transitory media for use with a data processing system, such as USBmemory, hard drive, electronic media or CD-ROM. The code may bedistributed on such media, or may be distributed to users from thememory or storage of one computer system over a network of some type tostorage devices on other computer systems for use by users of such othersystems.

Embodiments of the invention enable identifying cardiac structuresduring the medical procedure. When the position of the coronary sinus isaccurately known based on fluoroscopy of a coronary sinus catheter, itsposition can be related to the position of other portions of the heartprovided there is a common coordinate system to locate the otherportions, the embodiments of the invention place the coronary sinus, asdetermined from fluoroscopy, in registration with a 3-dimensional modelof the heart prepared using another imaging modality.

System Overview

Turning now to the drawings, reference is initially made to FIG. 1,which is a pictorial illustration of a system 10 for performingcatheterization procedures on a heart 12 of a living subject, which isconstructed and operative in accordance with a disclosed embodiment ofthe invention. The system comprises a catheter 14, which ispercutaneously inserted by an operator 16 through the patient's vascularsystem into a chamber or vascular structure of the heart 12. Theoperator 16, who is typically a physician, brings the catheter's distaltip 18 into contact with the heart wall at an ablation target site.Electrical activation maps, anatomic positional information, i.e., ofthe distal portion of the catheter, and other functional images may thenbe prepared using a processor 23 located in a console 24, according tothe methods disclosed in U.S. Pat. Nos. 6,226,542, and 6,301,496, and incommonly assigned U.S. Pat. No. 6,892,091, whose disclosures are hereinincorporated by reference. One commercial product embodying elements ofthe system 10 is available as the CARTO® 3 System, available fromBiosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, Calif.91765, which is capable of producing electroanatomic maps of the heartas required for the ablation. This system may be modified by thoseskilled in the art to embody the principles of the invention describedherein.

Areas determined to be abnormal, for example by evaluation of theelectrical activation maps, can be ablated by application of thermalenergy, e.g., by passage of radiofrequency electrical current throughwires in the catheter to one or more electrodes at the distal tip 18,which apply the radiofrequency energy to the myocardium. The energy isabsorbed in the tissue, heating (or cooling) it to a point (typicallyabout 60° C.) at which it permanently loses its electrical excitability.When successful, this procedure creates non-conducting lesions in thecardiac tissue, which disrupt the abnormal electrical pathway causingthe arrhythmia. The principles of the invention can be applied todifferent heart chambers to treat many different cardiac arrhythmias.

The catheter 14 typically comprises a handle 20, having suitablecontrols on the handle to enable the operator 16 to steer, position andorient the distal end of the catheter as desired for the ablation. Toaid the operator 16, the distal portion of the catheter 14 containsposition sensors (not shown) that provide signals to a positioningprocessor 22, located in the console 24.

Ablation energy and electrical signals can be conveyed to and from theheart 12 through the catheter tip and/or one or more ablation electrodes32 located at or near the distal tip 18 via cable 34 to the console 24.Pacing signals and other control signals may be conveyed from theconsole 24 through the cable 34 and the electrodes 32 to the heart 12.Sensing electrodes 33, also connected to the console 24 are disposedbetween the ablation electrodes 32 and have connections to the cable 34.

Wire connections 35 link the console 24 with body surface electrodes 30and other components of a positioning sub-system. The electrodes 32 andthe body surface electrodes 30 may be used to measure tissue impedanceat the ablation site as taught in U.S. Pat. No. 7,536,218, issued toGovari et al., which is herein incorporated by reference. A temperaturesensor (not shown), typically a thermocouple or thermistor, may bemounted on or near each of the electrodes 32.

The console 24 typically contains one or more ablation power generators25. The catheter 14 may be adapted to conduct ablative energy to theheart using any known ablation technique, e.g., radiofrequency energy,ultrasound energy, freezing technique and laser-produced light energy.Such methods are disclosed in commonly assigned U.S. Pat. Nos.6,814,733, 6,997,924, and 7,156,816, which are herein incorporated byreference.

The positioning processor 22 is an element of a positioning subsystem inthe system 10 that measures location and orientation coordinates of thecatheter 14.

In one embodiment, the positioning subsystem comprises a magneticposition tracking arrangement that determines the position andorientation of the catheter 14 by generating magnetic fields in apredefined working volume and sensing these fields at the catheter,using field generating coils 28. The positioning subsystem may employimpedance measurement, as taught, for example in U.S. Pat. No.7,756,576, which is hereby incorporated by reference, and in theabove-noted U.S. Pat. No. 7,536,218.

A fluoroscopic imaging device 37 has a C-arm 39, an x-ray source 41, animage intensifier module 43 and an adjustable collimator 45. A controlprocessor (not shown), which may be located in the console 24, allows anoperator to control the operation of the fluoroscopic imaging device 37,for example by setting imaging parameters, and controlling thecollimator 45 to adjust the size and position of the field of view. Thecontrol processor may communicate with the fluoroscopic imaging device37 via a cable 51 to enable and disable the x-ray source 41 or restrictits emissions to a desired region of interest by controlling thecollimator 45, and to acquire image data from the image intensifiermodule 43. An optional display monitor 49, linked to the controlprocessor, allows the operator to view images produced by thefluoroscopic imaging device 37. When the display monitor 49 is notincluded, the fluoroscopic images may be viewed on a monitor 29, eithervia a split screen or in alternation with other non-fluoroscopic images.

As noted above, the catheter 14 is coupled to the console 24, whichenables the operator 16 to observe and regulate the functions of thecatheter 14. The processor 23 is typically a computer with appropriatesignal processing circuits. The processor 23 is coupled to drive themonitor 29. The signal processing circuits typically receive, amplify,filter and digitize signals from the catheter 14, including signalsgenerated by the above-noted sensors and a plurality of location sensingelectrodes (not shown) located distally in the catheter 14. Thedigitized signals are received and used by the console 24 and thepositioning system to compute the position and orientation of thecatheter 14 and analyze the electrical signals from the electrodes, andgenerate desired electroanatomic maps.

Typically, the system 10 includes other elements, which are not shown inthe figures for the sake of simplicity. For example, the system 10 mayinclude an electrocardiogram (ECG) monitor, coupled to receive signalsfrom one or more body surface electrodes, to provide an ECGsynchronization signal to the console 24. As mentioned above, the system10 typically also includes a reference position sensor, either on anexternally-applied reference patch attached to the exterior of thesubject's body, or on an internally-placed catheter, which is insertedinto the heart 12 maintained in a fixed position relative to the heart12. Conventional pumps and lines for circulating liquids through thecatheter 14 for cooling the ablation site are provided.

Operation

Reference is now made to FIG. 2, which is a flow-chart of a method ofregistration of cardiac images using a coronary sinus catheter inaccordance with an embodiment of the invention. The process steps areshown in a particular linear sequence for clarity of presentation.However, it will be evident that many of them can be performed inparallel, asynchronously, or in different orders. Those skilled in theart will also appreciate that a process could alternatively berepresented as a number of interrelated states or events, e.g., in astate diagram. Moreover, not all illustrated process steps may berequired to implement the method.

At initial step 53 a CT (or MRI) image of the heart is obtained. Thismay be accomplished prior to the current session, but in any case priorto introduction of a cardiac catheter. The image created in this stephas a scale and coordinate system that is specific to the imageacquisition device employed, which is referred to for convenience as “CTcoordinates”. The term “CT coordinate space” describes a 3-dimensionalspace having points described in CT coordinates. The coronary sinus isdefined in CT coordinates on the image.

Next, at step 71 the CT image is imported into an image processingcomputer, e.g., the above-described CARTO 3 system. At this stage, theimported image occupies CT coordinate space. However, images normallyproduced using the image processing computer have another coordinatesystem and occupy a different coordinate space. This coordinate systemand space are referred to herein for convenience as “CARTO coordinates”and “CARTO coordinate space”, respectively. It will be understood thatthe use of this terminology does not limit the application of the methodto the CARTO 3 system. Rather the steps may be performed by many othertypes of image processing computers.

Next at step 55, using the image processing computer of step 71, a3-dimensional model of the heart in CT coordinate space is prepared fromthe CT image. This can be done using the CARTOMERGE™ module, availablefrom Biosense Webster.

Next, at step 73 a coronary sinus catheter is introduced into thecoronary sinus under fluoroscopic control.

Next, at step 75, with the coronary sinus catheter in place, thecoronary sinus is reconstructed by the image processing computer usingthe techniques taught in commonly assigned copending application Ser.Nos. 14/621,570 and 14/621,581, which are herein incorporated byreference. Briefly, a 3-dimensional path of the coronary sinus cathetermay be estimated using epi-polar geometry or iterative reconstruction oflinear segments. In one method of reconstructing the coronary sinus, thepatient's heart position is tracked over time. In order to compensatefor heart movement, an algorithm reconstructs a path or track of thecoronary sinus catheter in three dimensions, based on two 2-dimensionalfluoroscopic images acquired before and after a movement, andsynchronized in the cardiorespiratory cycle. A transformation betweenthe two reconstructed catheters is computed and used to align the data.The reconstructed coronary sinus is motion-compensated, and exists inCARTO coordinate space.

Reference is now made to FIG. 3, which is a composite image illustratinga stage in the process of coronary sinus reconstruction as applied to a3-dimensional model 81 of the heart as described in step 55, inaccordance with an embodiment of the invention. In the lower portion ofthe figure, taken from a fluoroscopic frame, a corridor 83 is outlinedand sampled around a CS catheter path 85 (represented by a broken line).The catheter path 85 was defined from previous frame and may have beenannotated by a human operator. The divergence of CS catheter 87 from thecatheter path 85 is compensated by suitable transformations, asexplained in further detail in the above-noted application Ser. Nos.14/621,570 and 14/621,581,

Referring again to FIG. 2 together with FIG. 3, at step 77 thereconstructed coronary sinus is placed in registration with the3-dimensional model that was prepared in step 55 by aligning coronarysinus 89 in the model 81 with the transformed catheter path 85 obtainedfrom analysis of the fluoroscopic image. It will be recalled that the3-dimensional model 81 exists in CT coordinate space. The model 81 isnow transformed into CARTO coordinate space. The CARTOMERGE™ imageintegration module, available from Biosense Webster, is suitable forperforming the image registration and coordinate transformation. Sincethe position or the coronary sinus is closely related to the position ofother portions of the heart, the remainder of the heart on the model 81will be in registration with other cardiac images generated anddisplayed by the image processing computer.

Then in final step 79, the coronary sinus and the other cardiacstructures can now be accurately located on the image processingcomputer display in CARTO coordinate space.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and sub-combinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. A method, comprising the steps of: importing image data of a heart ofa living subject into an image-processing computer system, the hearthaving a coronary sinus; representing the image data as a first model ofthe heart in a first coordinate space, the first model comprising thecoronary sinus; introducing a probe into the coronary sinus; thereafteracquiring fluoroscopic image data of the probe; using the fluoroscopicimage data to prepare a second model of the coronary sinus in a secondcoordinate space; and transforming the first model into the secondcoordinate space by placing the coronary sinus of the second model inregistration with the coronary sinus of the first model.
 2. The methodaccording to claim 1, wherein the image data is obtained by computedtomography of the heart.
 3. The method according to claim 1, wherein theimage data is obtained from magnetic resonance imaging of the heart. 4.The method according to claim 1, wherein the first model is a3-dimensional model.
 5. The method according to claim 1, whereinpreparing a second model comprises reconstructing a 2-dimensional pathof the probe.
 6. The method according to claim 5, wherein preparing asecond model comprises estimating a 3-dimensional path of the probe fromthe 2-dimensional path.
 7. The method according to claim 1, furthercomprising locating a cardiac structure in the transformed first modelin the second coordinate space.
 8. An apparatus, comprising: a cardiaccatheter adapted for introduction into a coronary sinus of a heart of aliving subject; a display; and a processor, which is cooperative with afluoroscopic imaging device for performing the steps of: importing imagedata of the heart; representing the image data as a first model of theheart in a first coordinate space, the first model comprising thecoronary sinus; introducing a probe into the coronary sinus; thereafteracquiring fluoroscopic image data of the probe; using the fluoroscopicimage data to prepare a second model of the coronary sinus in a secondcoordinate space; and transforming the first model into the secondcoordinate space by placing the coronary sinus of the second model inregistration with the coronary sinus of the first model.
 9. Theapparatus according to claim 8, wherein the image data is obtained bycomputed tomography of the heart.
 10. The apparatus according to claim8, wherein the image data is obtained from magnetic resonance imaging ofthe heart.
 11. The apparatus according to claim 8, wherein the firstmodel is a 3-dimensional model.
 12. The apparatus according to claim 8,wherein preparing a second model comprises reconstructing a2-dimensional path of the probe.
 13. The apparatus according to claim12, wherein preparing a second model comprises estimating a3-dimensional path of the probe from the 2-dimensional path.
 14. Theapparatus according to claim 8, further comprising locating a cardiacstructure in the transformed first model in the second coordinate space.